Biopharmaceuticals such as protein drugs, vaccines etc are usually manufactured by cell culture and purified downstream by chromatography and other methods. Before the downstream purification, all particulates from the cell culture such as cells, cell debris etc must be removed in one or more clarification steps. At least one of these clarification steps normally involves depth filtration and to obtain a good clarification result with minimum clogging of the filter material, serial filtration through depth filter materials with decreasing pore size ratings is commonly used.
Stackable depth filter cassettes or capsules provide convenience for the user compared to traditional lenticular filter stacks in reusable housings. Several such stackable cassettes/capsules have been disclosed, see e.g. US20100282663, EP1967244A1, etc. They often contain a series of depth filter materials with decreasing pore size in each cassette/capsule to decrease clogging of the finer filter materials and there are also limited possibilities of combining different filter materials within stacks.
As the properties of bioprocess feeds can vary dramatically depending on the cell type used, the cell culture conditions, any pretreatments before depth filter clarification etc, there is a high demand for flexibility in the design of depth filtration setups in order to provide efficient clarification without severe clogging and at the same time minimizing the filter surface used to keep costs down. Current cassettes and capsules have limitations in this respect in that they only provide fixed 1:1 area ratios between coarse and fine filters, which leads to overdimensioning of one filter type and possibly underdimensioning of the other type. This leads to inefficient filtration processes and accordingly there is a need to provide a cassette or capsule system with improved flexibility.